Piping parallel devices - not correct pressuredrop critical path missing

[HVAC-Novice]

I have 2 boilers in parallel. when I only connect boiler 2 All flow goes through it (Connector is set to calculate) and system pressure is 9.9 psi. when I connect B-1  for some reason all flow still went through B-2 and 0 flow to B-1. but the system pressure is 7.47 psi only. In the pressure loss report I found out, it is missing the last leg to the boiler (inc. boiler, and the isolation and control valve).  Then I changed the boiler connector flow to "system" and assigned it a flow of 1 for each boiler. this somehow improved things, but it only shows 8.53 psi. but it doesn't include the boiler leg (valves, boiler) in the pressure report. the reason it is so high is that setting both boilers to 1-systme flow is, on the upstream pipe it doubles the flow. So I set each boiler flow to 0.5. that gives me 7.47 again. so basically normal flow in the system, but the boiler leg is not included. 

In all scenarios with both boilers connected (flow based on system flow, or connected) the system inspector doesn't show the critical path going through the boiler. In reality at full load both boilers will operate, so there is only half flow through each boiler. But if one boiler fails, all flow could go through one and I like to use that pressure for pump sizing.

How do I force the critical path to include the boiler when both are connected? I'll have 2 pumps in parallel and suspect will have the same issue there. One dirty workaround would be to not actually connect the pipe of the second boiler. I use R2023 and wasn't able to use the hydraulic separation. 

[HVAC-Novice]

I fond part of my problem may be the "Tee".  If i only use one boiler and use a 90°, all is fine and the critical path goes through the boiler. but if I make the 90 to a Tee (and cap it) the flow in the boiler leg is negative and does not get included in the critical path. I tried several of the oob Tees with he same problem. 

the problem is similar where i have 2 parallel pumps. The critical path basically stops at the first Tee (the one that splits to the 2 pumps)

[HVAC-Novice]

Some progress with cheating. 

where i circled red i broke the pipe and capped the Tee (so no flow goes to the second pump in the back). the pumps are set to use the system flow and the one in the critical path is set to 1, the other to 0. 

I was hoping to actually connect the pipe and then do the hydraulic separation. But no matter what I do, the hydraulic separation symbol stays grayed out (under Modify pipes). i never used that before and tried to follow the help instructions. But no dice. is there some trick? 

My plan right now basically is to use hydraulic separation for the pumps and boilers. if that fails, I fake it and cap the pipe and just make it look like the second pump and boiler are connected. but ideally I don't have to fake it. 

[iainsavage]

I think it depends on whether you are calculating pressure loss for the whole supply and return loop, or calculating the supply separately then the return separately and manually adding them together.

Note the restrictions for calculating hydronic loops:

"A closed loop hydronic piping network must contain:

• A single pump/circulator
• A single source, such as a boiler
• Multiple piping segments
• Multiple terminals, such as radiators."